I have a situation where there’s a 3rd party in my relationship (my boyfriends ex) and I feel she has a strong negative hold on him. I wanted to know if there is a way to rid her negative energy. Like some prayer that I could say or a ritual that I could do to get rid of her negative energy or even her out of our life?

Be extremely present and appreciate life for everything it is. Nothing can get more positive than gratefulness.
Unfortunately you can’t MaKe someone else be positive or negative, unless they get the vibe from you.